The present invention generally pertains to injection molding of hollow plastic products and is particularly directed to an improved mold and method for molding and controlling the dimensions of hollow plastic products having side walls.
In U.S. Pat. No. 4,508,676 to the present inventor, there is generally described a mold and method for molding and controlling the dimensions of hollow plastic products having side walls. The mold described herein includes a first mold part and a second mold part defining a mold cavity therebetween, encompassed by a parting line, for forming the hollow plastic product, and further defining a gate for admitting molten injected plastic into the cavity. One of the mold parts includes a retractable portion adjacent the gate, with the retractable portion being movable between a protracted position and a retracted position while the mold is closed; and the mold parts define primary flow channels extending from the gate, which, when the retractable portion of the one mold part is protracted, direct initially injected molten plastic from the gate to create stabilizing regions of stiffened plastic, to thereby impede lateral deflection of the mold parts with respect to each other when additional molten plastic subsequently is injected, whereby the side walls of the molded plastic product are uniformly dimensioned.
A "flow channel" is defined as a portion of the mold cavity which directs the flow of molten plastic.
"Stiffened plastic" is defined as plastic that is no longer molten and has solidified sufficiently to impede lateral deflection of the mold parts.
In the mold described in U.S. Pat. No. 4,508,676, the mold cavity is centered about an axis, and the gate is axially disposed in the mold cavity. The portions of the mold parts that define the stabilized regions include portions that are approximately parallel to the axis of the mold cavity. Also, the retractable portion of the one mold part is an axially movable inner core section. The retractable portion is retracted by conventional means such as by hydraulic fluid acting upon the appropriate piston surfaces within a double-acting hydraulic cylinder.